Working on my Bus . . . again

knkreb on Sat August 21, 2004 11:21 PM

Okay, here's the scoop, from a few months ago. Gotta a Carrier Transicold evap EM14, and skirt mounted cond. coil CM2. It has the factory in-dash system, and factory HT6 compressor. HT6 does not have enough capacity to cool on a hot day. I have tons of capacity available from my condensor, according to some of the numbers I've seen come up on a few searches.

My rear evap seems to be keeping the suction pressure up too high I believe. It's rating is around 24-26000 BTU, and seems to be maxing out my capacity for the whole system. I have finally resorted to cranking down on the TXV and increase the superheat to help drop the suction pressure to get more cooling at least out of the factory dash system.

So, I'm looking at best way to fix situation. Looks like I need a condensor in front of radiator (ugh) and second compressor, and whole bunch of new hoses. What am I gonna have tied up in this system?

Let me ask this question first. The HT6 is in Yukons, and suburbans, etc from what I am told. This is a full size van, with a high top on it. (It's a handicap body that you can stand up and walk around in over six feet tall inside) Anyone have any idea what the heat load would be in this thing? It's about double the volume (estimated) of that of the Yukon/Suburban setup. Are we talking like almost 4 tons of a/c or what?

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DetroitAC on Mon August 23, 2004 11:39 AM

Hi Knkreb, I remember this topic from a while back...

What makes you say that you need a second condenser? Is your skirt mounted condenser barely up to the task now, and you expect things to get a lot worse when you get enough compressor in the bus?

A single automotive compressor would be able to keep up with that rear evaporator, but both evaps is quite a struggle.

Why not just get one compressor that is up to the task? Carrier Transicold and Thermoking make some really heavy, durable two piston compressors that go into transit busses, and touring coaches. I'm not sure about the pulleys available, they may not have any with automotive poly-v serpentine pulleys.

Two automotive compressors in parallel is a possibility, but you must do some clever stuff to make sure that both pumps get oil flowing to them. You could build an oil separator, and then guarantee that oil flows back, and you really wouldn't need the separator to be highly efficient, just need it to work somewhat. You could also build a suction muffler into the point where the two suction lines split and go to each compressor, and put both pipes into the can symmetrically. Really the most foolproof way would be to run the rear evap to one compressor, and the front evap to the other and two separate systems, but the downside...is two separate systems. Also fairly foolproof would be to use a common condenser (the skirt mount unit) and run the front suction line to one compressor, and the rear suction line to the other. PAG is miscible in R-134a liquid so each evap would be fed an equal amount of oil, so each compressor would be assured of lubrication. Not much simpler than two separate systems, but you only need one condenser.

It's very difficult to say what what your cooling load is on the bus, has a lot to do with internal thermal mass, body air leakage, and probably for this application door open time.

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